1. Field of the Invention
The present invention relates to a cell management method and apparatus, and in particular to a cell management method and apparatus for switching a cell over to an operating/nonoperating (active/inactive) state based on a cell usage rate and the like.
2. Description of the Related Art
Prior art examples of the above-mentioned cell management technology will now be described referring to FIGS. 18-21A, and 21B.
A wireless communication system 1 shown in FIG. 18 is composed of a core network 10, “l (el)” units of exchanges 20_1-20—l(hereinafter, occasionally represented by a reference numeral 20) connected to the core network 10, “m” units of wireless network control apparatuses 30_1-30—m (hereinafter, occasionally represented by a reference numeral 30) connected to the exchange 20, and “n” units of base stations 40_1-40—n (hereinafter, occasionally represented by a reference numeral 40) managed by the wireless network control apparatuses 30.
The communication of voice data and packet data in the wireless communication system 1 is performed, as shown in FIG. 19. Each of mobile stations 50_1-50—k (hereinafter, occasionally represented by a reference numeral 50), which exists within cover areas AR1-ARn (hereinafter, occasionally represented by reference characters AR) where the base stations 40_1-40—n can respectively provide services, connects a call to the wireless network control apparatus 30 through the base station 40 of the cover area AR where the mobile station itself exists.
Also, as shown in FIG. 19, a plurality of cells CL divided according to a frequency and a directivity to be assigned are allocated within the cover area AR for an effective use of the area. Accordingly, more mobile stations 50 are allowed to connect their calls within a single cover area AR.
However, the number of mobile stations capable of connecting a call per cell CL is limited, and the number of cells CL (hereinafter, referred to as upper limit number of operating cells) that can be made an operating state for the entire system is also limited, so that an operator presets cells CL to be respectively made an operating state and a nonoperating state (hereinafter, respectively referred to as operating cell CLw and nonoperating cell CLp) according to a regionality (e.g. user number density) and the like of the cover area AR at the time of network configuration.
Thereafter, at the time of network operation, the operator carries out a reappraisal of the operating cell CLw and the nonoperating cell CLp according to a transition of communication traffic and the like, and switches between an operating and a nonoperating state thereof as appropriate.
In such a network operation, problems of a call loss occurrence and a network load increase may arise.
Example of Call Loss Occurrence: FIG. 19
It is now assumed that two operating cells CLw, for example, are set as shown hatched in the cover area AR6 of the base station 40_6 shown in FIG. 19.
Within this cover area AR6, when the mobile stations 50_7-50—k (“k” is a number sufficiently larger than the limited number of mobile stations capable of connecting a call per cell CL) request call connections at the same time, cell usage rates of these operating cells CLw increase so that the number of mobile stations exceeds the limited number. Accordingly, some of the mobile stations cannot make the call connections to the wireless network control apparatus 30_2, thereby generating a call loss as shown in FIG. 19.
Example of Network Load Increase: FIG. 20
The above-mentioned call loss occurrence can be prevented if the operator presets all of the cells CL within the cover area AR as the operating cells CLw.
However, an increase in a density of operating cells within the cover area AR leads to a rash of handovers associated with moves of the mobile stations 50 between the operating cells CLw, so that an increase in communication traffic by location registration signals and the like causes a network load increase for the exchanges 20 and the wireless network control apparatuses 30. Also, the installation of the exchanges 20 and the wireless network control apparatuses 30 resistant to the network load increase leads to an increase in development cost and operation cost.
In order to deal with these problems, a cell management technology described below has been proposed.
Prior Art Cell Management Example: FIGS. 21A and 21B
FIG. 21A shows a part of the wireless network control apparatus 30_1 as well as the base stations 40_1 and 40_2 extracted from the arrangement of the wireless communication system 1 shown in FIG. 18.
In the cover areas AR1 and AR2 of the base stations 40_1 and 40_2, operating cells CLw_001-CLw_019 and CLw_020-CLw_038 divided according to directivities are respectively set. Also, as the operating cells CLw_001-CLw_003 are exemplified in FIG. 21B, a frequency Fo as a working frequency is allocated to the operating cells CLw_001-CLw_003. Nonoperating cells CLp_101-CLp_103 and CLp_201-CLp_203 having the same directivity as that of the operating cells CLw_001-CLw_003 while having protection frequencies F1 and F2 different from the working frequency Fo are respectively allocated thereto are set.
In operation, the wireless network control apparatus 30_1 controls the network by using the operating cells CLw_001-CLw_003, while on the other hand monitoring the cell usage rates of the operating cells CLw_001-CLw_003, and additionally using, when the cell usage rates exceed a preset upper limit value (hereinafter, referred to as high-load state), the nonoperating cells CLp_101-CLp_103 and CLp_201-CLp_203 by switching them over to the operating state. Also, when the cell usage rates of the nonoperating cells CLp_101-CLp_103 and CLp_201-CLp_203 that have been made the operating state decrease below a preset lower limit value (hereinafter, referred to as low-load state), the wireless network apparatus 30_1 stops using the nonoperating cells CLp_101-CLp_103 and CLp_201-CLp_203 and switches them over again to the nonoperating state.
Thus, by using cells CL to which the protection frequencies are allocated, it is made possible to prevent the above-mentioned call loss occurrence without unnecessarily increasing the network load (see e.g. patent document 1).
It is to be noted that, as a reference example, there is a technology that reduces a coverage of signals communicated between the base stations 40 and the mobile stations 50 (namely, reduces the number of mobile stations existing within the operating cells CLw), thereby decreasing the cell usage rate to maintain the communication quality at a fixed level (see e.g. patent document 2).
Although this reference example can maintain the communication quality at a fixed level, the number of mobile stations capable of making call connections in the operating cells CLw is further limited when the cell usage rates are increased. Therefore, the above-mentioned call loss occurrence cannot be prevented.    [Patent document 1] Japanese Patent Application Laid-open No. 5-316039    [Patent document 2] Japanese Patent Application Laid-open No. 2000-50340
In the above-mentioned prior art example, while the call loss occurrence can be prevented by using a protection frequency bandwidth, protection frequencies cannot always be allocated thereto since limitations exist for a frequency bandwidth available in a wireless communication system (for example, a limitation by a distribution of frequency bandwidths among enterprises operating similar wireless communication systems and a limitation by frequency bandwidths used by other communication apparatuses, systems, and the like). Accordingly, in the above-mentioned prior art example, there is a problem that in the presence of a limitation for available frequency bandwidths, the call loss may be generated by failing to secure the number of operating cells for the mobile stations requesting call connections when the cell usage rates are increased without being able to prepare sufficient nonoperating cells to which protection frequency bandwidths are allocated.